Sequential elucidation of the β-Ca3(PO4)2/TiO2 composite development from the solution precursors

Abstract

The sequential formation of β-Ca₃(PO₄)₂/TiO₂ composites with assorted ratios synthesized from the solution precursors is described. The phase evolution of the synthesized powders to yield a composite during progressive heat treatments is determined through a set of analytical techniques. Investigation reveals the initial crystallization of apatite and anatase TiO₂ (a-TiO₂) mixtures at <800 °C. β-Ca₃(PO₄)₂ crystallizes at ∼800 °C and its subsequent stability is retained until 1300 °C. Besides, a gradual phase transition of a- → rutile TiO₂ (r-TiO₂) transpires in the range of 800–1000 °C before the complete r-TiO₂ transformation accomplishes at 1100 °C. The structural stability of the resultant β-Ca₃(PO₄)₂/r-TiO₂ composites is retained until 1300 °C. The β-Ca₃(PO₄)₂ lattice also hosts a selective amount of Ti⁴⁺ and as a consequence the anticipated β- → α-Ca₃(PO₄)₂ conversion that occurs at 1180 °C is delayed. TiO₂ plays a crucial role in the attainment of dense and pore free microstructures of β-Ca₃(PO₄)₂/r-TiO₂ composites. The mechanical properties determined through nanoindentation revealed an upsurge trend as a function of TiO₂ content in the composites.